1. Field of the Invention
The present invention relates generally to the manufacturing of optical fibers, and particularly to manufacturing a fluorine doped preform from which an optical fiber may be drawn from the preform.
2. Technical Background
Optical fibers have acquired an increasingly important role in the field of communications, frequently replacing existing copper wires. This trend has had a significant impact in the local area networks (i.e., for fiber-to-home uses), which has seen a vast increase in the usage of optical fibers. Further increases in the use of optical fibers in local loop telephone and cable TV service are expected, as local fiber networks are established to deliver ever greater volumes of information in the form of data, audio, and video signals to residential and commercial users. In addition, use of optical fibers in home and commercial business environments for internal data, voice, and video communications has begun and is expected to increase.
Optical fibers having a fluorine doped region have unique attributes in the areas of long haul optical fibers, dispersion compensating optical fibers, dispersion slope compensating optical fibers, and high data rate optical fibers. The ability to include fluorine in a preform is an important aspect of producing an optical fiber with a fluorine doped region.
Prior attempts to incorporate fluorine into the preform include depositing fluorine doped soot on a starting member. Typically, the starting member was a sintered core cane. However, in the past, deposited fluorine has exhibited significant migration from the region or regions of interest and loss, such that depositing fluorinated soot was not a practical manner to produce a fluorinated soot preform. Preforms fluorinated during deposition have exhibited a fluorine loss between forty (40%) percent to fifty (50%) percent. One reason for the low retention rate of fluorine is the production of the compound SiF4 during manufacturing. Typically SiF4 generated during manufacturing will volatilize off.
Furthermore deposition of fluorine also has not been able to achieve the necessary moat depth for optical fibers that require a region with a weight percent of fluorine of at least 1.0% at a practical deposition rate. For example, to achieve a weight of 2.5% fluorine, in the past the fluorinated soot has been deposited at a rate of 0.2 g/min or less, whereas, non-fluorine doped soot can be deposited at a rate of greater than about 2 grams per minute. Generally as the amount of fluorine desired to be incorporated into the soot preform increases, the deposition rate of the fluorinated soot decreases. This is very troublesome, for the reason that many of the dispersion managed fibers require the fiber to have a region with a fluorine weight percent of at least about 3.0%.
Additionally, during the production of fluorine doped soot at traditional rates of soot deposition, an etching reaction can occur. The etching reaction retards soot nucleation and likewise inhibits the soot deposition rate.
Another issue with the deposition of fluorine doped soot is pollution abatement. Fluorine deposition process creates soot particles, which include one or more fluorine atoms. The separation of the fluorine from the soot particles is a costly and timely process.
A fluorine doping method is needed that enables deeper moat levels which does not reduce deposition rates to impractical levels and that enables less costly methods of pollution abatement.
One aspect of the present invention is a method of making an optical fiber containing a fluorine doped region. The method includes reacting a fluorine containing precursor in a flame of a combustion burner without forming a soot, thereby forming a fluorine doping atmosphere.
Another aspect of the invention includes a method of doping an optical fiber preform. The second method includes reacting at least a fluorine containing precursor in a flame of a combustion burner, wherein the precursors reacted in the flame are substantially devoid of the element of silicon, thereby forming a fluorine containing atmosphere for the doping of a soot preform.
An additional aspect of the invention is a method of making an optical fiber. This method includes the steps of: (1) reacting at least one precursor in the flame of a combustion burner, wherein said precursors comprise at least one fluorine containing compound and said precursors are substantially free of any silicon containing compound capable of forming a soot particle, and (2) directing a reaction product of said reacting step toward a soot preform.
Practicing the described aspects of the invention will result in the advantage of producing a fluorine doped soot preform in just one deposition step. A further advantage that will result from practicing the above methods is an efficient use of fluorine. Additional advantages of the invention include the ability to achieve high doping levels, the ability to achieve fast deposition and process rates, efficient use of precursors, and lower pollution abatement costs. The aforementioned invention may be used to preferentially dope a soot preform with fluorine and not dope fluorine dope soot particles in the flame of a burner.
Practicing the aforementioned aspects of the invention can be used to produce a fluorine doped soot preform that is doped during deposition. The above method may be used to improve the uniformity of the refractive index of a fluorine doped region of the preform. Other advantages of practicing the above method include incorporating into the preform an increased amount of fluorine dopant and less of the dopant is lost in the effluent, and the drawn fiber may exhibit deeper index profiles than fibers previously fluorinated during deposition. The above methods of the invention may be used to produce an optical fiber with a fluorine doped section having a delta (xcex94) of at least about xe2x88x920.35% or more negative. The above methods may be practiced to produce a fiber with a fluorine doped region having at least about 1.5 weight percent of fluorine, more preferably at least about 3.0 weight percent of fluorine.
Additional advantages that will result from practicing the described aspects of the invention is that the fiber may be formed with a minimal number of transfers steps, the perform is not doped during consolidation, the preform is not doped during sintering, high concentrations of HF can be formed which will result in higher fluorine concentrations in the preform, the partial pressure of HF in the doping atmosphere may be maintained substantially constant, the temperature of the burner may be optimized to favor the formation of HF, surface area, in terms of area per mass, may be optimized for incorporating F into the soot preform, and HF is a suitable compound for water based pollution remediation techniques.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from that description or recognized by practicing the invention as described herein, including the detailed description which follows, the claims, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework for understanding the nature and character of the invention as it is claimed. The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate various embodiments of the invention, and together with the description serve to explain the principles and operation of the invention.